This roast lamb with fennel and mustard butter is a delicious and flavorful dish that is perfect for a special occasion or a Sunday roast. The lamb is seasoned with a mixture of fennel seeds, garlic, and rosemary, then roasted to perfection. The fennel and mustard butter adds a tangy and aromatic flavor to the lamb, making it incredibly tender and juicy. Serve this dish with roasted potatoes and a side of green vegetables for a complete and satisfying meal.